### RF Designer - Components (Ideal Transmission Line Elements)

Posted:

**Wed Jan 07, 2015 4:45 am**Ideal Transmission Line Elements

TLIN - Ideal Transmission Line

Model for an ideal and lossless transmission line. Electrical length (EL) is specified in degrees or radians at frequency F0.

TLOC - Ideal Open Circuited Transmission Line

Model for an ideal and lossless open circuited transmission line. Electrical length (EL) is specified in degrees or radians at frequency F0.

TLSC - Ideal Short Circuited Transmission Line

Model for an ideal and lossless short circuited transmission line. Electrical length (EL) is specified in degrees or radians at frequency F0.

TLIN4 - Ideal 4 Node Transmission Line

Model for an ideal and lossless transmission line with the ground terminals left open and available as ports in the schematic. Electrical length (EL) is specified in degrees or radians at frequency F0.

CLIN - Ideal Coupled Transmission Line

Model for a pair of lossless symmetric coupled transmission lines. Electrical length is specified in degrees or radians at frequency F0. Coupling is determined by the even and odd mode impedances (Zoe and Zoo).

Given a desired coupling C in decibels, Zoe = Zo * sqrt((1 + k) / (1 - k)) where k = power(10.0, -C/20.0). Zoo can the be found by solving Zoo = Zo * sqrt((1 - k) / (1 + k))

Example: Find Zoe and Zoo for a 10 dB coupler in a 50 ohm system.

First calculate k as k = power(10.0, -10/20) = 0.316

Zoe is found as Zoe = Zo * sqrt((1 + .316) / (1 - .316)) = 69.4 ohms

Zoo is found as Zoo = Zo * sqrt((1 - .316) / (1 + .316)) = 36 ohms

TLIN - Ideal Transmission Line

Name | Description | Units | Default Value |

Z | Impedance | Resistance | 50 ohms |

EL | Electrical length | Degrees | 90º |

F0 | Frequency where EL is specified | Frequency | 1000 MHz |

Model for an ideal and lossless transmission line. Electrical length (EL) is specified in degrees or radians at frequency F0.

TLOC - Ideal Open Circuited Transmission Line

Name | Description | Units | Default Value |

Z | Impedance | Resistance | 50 ohms |

EL | Electrical length | Degrees | 45º |

F0 | Frequency where EL is specified | Frequency | 1000 MHz |

Model for an ideal and lossless open circuited transmission line. Electrical length (EL) is specified in degrees or radians at frequency F0.

TLSC - Ideal Short Circuited Transmission Line

Name | Description | Units | Default Value |

Z | Impedance | Resistance | 50 ohms |

EL | Electrical length | Degrees | 45º |

F0 | Frequency where EL is specified | Frequency | 1000 MHz |

Model for an ideal and lossless short circuited transmission line. Electrical length (EL) is specified in degrees or radians at frequency F0.

TLIN4 - Ideal 4 Node Transmission Line

Name | Description | Units | Default Value |

Z | Impedance | Resistance | 50 ohms |

EL | Electrical length | Degrees | 90º |

F0 | Frequency where EL is specified | Frequency | 1000 MHz |

Model for an ideal and lossless transmission line with the ground terminals left open and available as ports in the schematic. Electrical length (EL) is specified in degrees or radians at frequency F0.

CLIN - Ideal Coupled Transmission Line

Name | Description | Units | Default Value |

Zoe | Even-mode impedance | Resistance | 69 ohms |

Zoo | Odd-mode impedance | Resistance | 36 ohms |

EL | Electrical length | Degrees | 90º |

F0 | Frequency where EL is specified | Frequency | 1000 MHz |

Model for a pair of lossless symmetric coupled transmission lines. Electrical length is specified in degrees or radians at frequency F0. Coupling is determined by the even and odd mode impedances (Zoe and Zoo).

Given a desired coupling C in decibels, Zoe = Zo * sqrt((1 + k) / (1 - k)) where k = power(10.0, -C/20.0). Zoo can the be found by solving Zoo = Zo * sqrt((1 - k) / (1 + k))

Example: Find Zoe and Zoo for a 10 dB coupler in a 50 ohm system.

First calculate k as k = power(10.0, -10/20) = 0.316

Zoe is found as Zoe = Zo * sqrt((1 + .316) / (1 - .316)) = 69.4 ohms

Zoo is found as Zoo = Zo * sqrt((1 - .316) / (1 + .316)) = 36 ohms